Which tyres on which rims?

[XLR Motorsport]

I have two sets of rims for my FWD track car, 15" and 16". Which is better, to have the wets/road tyres on the 15" and the slicks/semi slicks on the 16" or the other way round?

Futhermore, the car is currently running 205/50 on the 16s but the fronts catch on the wheel arch on full lock, so can I get away with 195/45/16? And could I get away with running 225s on either the 15" or 16" wheels?

I'm considering Nankang AR-1s or slicks and either Avon ZV7s or Uniroyal Rainsport 5s. Advice is very welcome.

TIA